1. Field
The present disclosure relates to a backlight unit and a method for controlling a light-emitting diode (LED), and more particularly to a backlight unit and a method for controlling an LED, which can prevent overheating through sensing of an internal temperature of an LED driving circuit.
2. Description of the Related Art
A shutter glass type three-dimensional (3D) LED backlight display alternately displays a left-eye image and a right-eye image on a screen. A shutter glass alternately transmits/intercepts a left-eye image and a right-eye image in synchronization with an image that is alternately displayed to realize a 3D image.
In this case, in order to minimize crosstalk of the left-eye image and the right-eye image, a backlight is driven with current having a smaller duty (i.e., duty cycle) in synchronization with the image. If the duty is reduced as described above, luminance of a display is decreased. Accordingly, in order to compensate for the decrease of luminance, a 3D current having a peak value that is several times higher than a peak value of a two-dimensional (2D) normal current is generated.
FIG. 1 is a diagram illustrating a waveform of a 2D current. Referring to FIG. 1, the duty of the 2D current may be maximally extended up to 100% while it performs pulse width modulation (PWM) dimming of the backlight in a predetermined period.
FIG. 2 is a diagram illustrating a waveform of a 3D current. Referring to FIG. 2, the peak value of the 3D current may be greatly increased in comparison to the peak value of the 2D normal current.
By contrast, the maximum duty of an on time range of the 3D current illustrated in FIG. 2 is limited in comparison to the maximum duty of an on time range of the 2D current illustrated in FIG. 1.
FIG. 3 is a diagram explaining the occurrence of fuming due to 3D current overload in a 3D mode. Referring to FIG. 3, the occurrence of fuming in respective elements of an LED driving circuit due to 3D current overload will be examined as follows.
During a 3D normal operation, a 3D overload occurs due to an error of a driving circuit or other systems at time ts. The temperature of an integrated circuit (IC) is increased from the overload occurrence time ts. At the same time, the temperature (L temperature) of an inductor that is an element of the LED driving circuit is increased.
If the L temperature reaches a limit temperature at time tf, the inductor starts fuming. At this time, since the threshold temperature Tjmax of the integrated circuit is much higher than the limit temperature of the inductor, an overheating prevention function in the integrated circuit does not operate, and thus a control unit is unable to control the operation of the LED driving circuit.
Accordingly, overcurrent flows through the LED driving circuit and thus internal elements of the LED driving circuit or a backlight unit itself may be damaged and may lead to the occurrence of a serious accident, such as a fire.
In the related art, Over-Temperature Protection (OTP) has been used to prevent the overheating. However, since the OTP is the last means for preventing damage of an internal chip due to the overheating, the corresponding threshold temperature is set to a maximally high temperature Tjmax.
Due to this, there is a great difference between the threshold temperature of the integrated circuit and the limit temperature of the LED driving circuit, and thus even at a temperature where the LED driving circuit is overheated due to overload, the integrated circuit cannot perform a normal operation to cause OTP not to operate. Due to this, there has been a problem in that fuming or fire first occurs in respective elements, for example, inductors or transistors, included in the LED driving circuit.